Heat sealed thermoformed container and method of making same

ABSTRACT

An open top thermoformed plastic container or package for food stuffs and the like which is formed with a depending rim particularly adapted to receive a snap-on reusable cover to help preserve any unused portion of the contents. When the container is initially formed and filled, a plastic film or sheet is heatsealed to its open top edge to preserve the contents for what may be a long period before initial or partial use. In the manufacturing and filling process, a plurality of the container bodies or cavities are formed simultaneously in a container sheet and all of them are covered by a single seal sheet or film. Then, the seal sheet is either fully or partially cut around each cavity so that the subsequent punching operation which severs each container from its sheet at its rim will not damage or tear the seal sheet at the container edge and thus destroy the airtight seal.

United States atent [72] Inventor Wendell B. Shearer Longmeadow, Mass. [21] Appl. No. 756,862 [22] Filed Sept. 3, 1968 [45] Patented June 15, 1971 [73] Assignee Package Machinery Company East Longmeadow, Mass.

[54] HEAT SEALED THERMOFORMED CONTAINER AND METHOD OF MAKING SAME 3 Claims, 4 Drawing Figs.

52 U.S. Cl 53/30, 53/27 [51] Int. Cl B65b 47/10 [50] Field oiSearch 53/30,27, 184, 42

[5 6] References Cited UNITED STATES PATENTS 3,238,691 3/1966 Miller etal. 53/l84X 3,348,358 lO/l967 Sternau ABSTRACT: An open top thermoformed plastic container or package for food stuffs and the like which is formed with a depending rim particularly adapted to receive a snap-on reusable cover to help preserve any unused portion of the contents. When the container is initially formed and filled, a plastic film or sheet is heat-sealed to its open top edge to preserve the contents for what may be a long period before initial or partial use. In the manufacturing and filling process, a plurality of the container bodies or cavities are formed simultaneously in a container sheet and all of them are covered bya single seal sheet or film. Then, the seal sheet is either fully or partially cut around each cavity so that the subsequent punching operation which severs each container from its sheet at its rim will not damage or tear the seal sheet at the container edge and thus destroy the airtight seal.

HEAT SEALED THERMOFORMED CONTAINER AND METHOD OF MAKING SAME BACKGROUND OF THE INVENTION A highly desirable and economical package or container for food stuffs is one that can be thermoformed in plastic and hermetically sealed to preserve the contents until initial use and then recovered to preserve any remaining portion of the contents for later us. While the contents of a therrnoformed open top container can be hermetically sealed and protected until initial use by a plastic film or cover sheet which is heat-sealed to the top edge of the container, after such film has once been removed it cannot be effectively reapplied. If the container is formed with a depending rim suitable to receive a snap-on cover, and no seal sheet or film is employed, a less than perfect seal is provided to protect the contents for what may be a relatively long period before initial use. However, a snap-on cover will provide the protection necessary to preserve the contents remaining after initial and partial use for the relatively short period that the container will be stored or refrigerated before later use.

These two considerations have suggested the provision of a combined package or container, i.e., one having a seal film that will remain in place until initial use and also having a snap-on reusable cover for protection and preservation of the contents until subsequent use. However, difficulty has been encountered in providing the composite or combined package on a mass production basis. That is, in order to provide a container suitable to receive a snap-on cover, it should be formed with a depending rim, and while a plurality of such containers can be so formed in a single container sheet, difficulty is encountered in heat sealing a seal sheet to the top of the container cavities and then punching out the individual containers without destroying the seal between them and the seal sheet.

In avoiding this difficulty, it has been the practice to form the containers, sever them from the container sheet, place an individual seal sheet over each container and heat seal it to the container edge. Utilizing this technique, the heat sealing can be accomplished either before or after a snap-on cover has been placed over the container, but in either event, the process is time consuming and uneconomical.

SUMMARY OF THE INVENTION It is the general object of the present invention to provide a thermoformed container with a heat sealed seal sheet and which is adapted to receive a snap-on cover in a process which involves forming a plurality of such containers or container cavities in a container sheet, covering all such cavities with a single seal sheet and heat sealing it to the upper edge of each cavity prior to severing the container cavities from the container sheet without destroying the airtight heat seal.

In fulfilling this general object, the container cavities are thermoformed with the desirable rim for a snap-on cove, and the seal sheet is at least partially severed around each cavity while still in the thermoforming machine and prior to blanking or punching the individual containers from the container sheet.

BRIEF DESCRIPTION OF THE DRAWING FIG. 1 is a top plan view of a schematically illustrated container sheet as it would appear in a thermoforming machine adapted to form containers according to this invention.

FIG, 2 is a side elevational view showing the said container sheet and a seal sheet as illustrated in FIG. 1.

FIG. 3 is an enlarged vertical cross-sectional view taken as indicated by the line 3-3 of FIG. 1.

FIG. 4 is another large cross-sectional view taken through a finished container and showing a snap-on cover which is adapted to be associated with the container.

DESCRIPTION OF THE PREFERRED EMBODIMENT In keeping with the present invention, a suitable thermoforming plastic sheet 10 is placed in a thermoforming machine for intermittent longitudinal movement from left-toright as viewed in FIGS. 1 and 2. The sheet is initially flat and it is subjected to heat in the thermoforming machine so that it will become plastic and formable. Then, in intermittent movement through the machine, as the sheet reaches a portion of the machine which may lie under the left-hand section of the sheet as shown in FIGS. 1 and 2, the sheet is drawn downwardly as by vacuum into thermoforming dies comprising a part of the machine. When drawn into the thermoforming dies, a plurality of container cavities C, C are formed in the sheet 10, all such cavity portions being interconnected by longitudinal and transverse web portions, W, W. The thermoforming machine dies are so constructed that each cavity C is relatively deep and each web portion W is also drawn downwardly from the normal plane of the sheet 10 thereby to form a depending rim 12 around each cavity C. Preferably, the container cavities C, C are formed in longitudinal rows and in transverse rows as shown and are spaced apart by the webs W, W which also extend longitudinally and transversely between the rows of container cavities.

In continued intermittent movement from Ieft-to-right, those portions of the sheet 10 defining the container cavities C, C will reach a section of the thermoforming machine wherein the plastic material defining the sheet and cavities has cooled sufficiently to receive the food stuff or other product or content 14 which is to be packaged. The filling of the container cavities C, C is schematically shown in FIG. 2.

After the material 14 has been placed in the container cavities C, C, all of the cavities are to be covered by a thin plastic seal sheet or film 16, the thickness of which has been greatly exaggerated in the drawing, particularly at FIGS. 3 and 4. The seal sheet 16 can conveniently be provided in a continuous web fed from a roll I8 around an applicator roll 20 over the top of the container sheet 10. After being applied, the seal sheet or film 16 is heat-sealed to the container sheet 10 at the top edge of each rim 12 at the periphery of each container cavity C as indicated at 22, 22 (FIGS. 3 and 4). The heat seal 22 extends entirely around the top edge of the rim 12 for each container cavity C so that the said container cavity will be hermetically sealed by the seal sheet or film 16. When the seal sheet has been applied and advanced with the container sheet 10 in the condition shown toward the right-hand end of FIGS. 1 and 2, the individual container cavities should be severed to provide containers or packages adapted to receive a snap-on cover such as the cover 24 shown in FIG. 4.

The container rims I2 are formed as shown or otherwise shaped to have an outer edge 26 adapted to releasably engage and retain the rim or skirt 28 of the reusable cover 24. In the illustrative embodiment shown, the snap-on cover 24 is provided with internal beaded portions 30, 30 which can be engaged beneath the edge 26 of the container rim 12 to hold the cover 24 firmly in place on a finished container C after it has been snapped on. However, the cover can easily be removed by lifting the edge of its skirt 28, the said cover being provided in a flexible plastic material.

As best shown in FIG. 3, each container must be blanked, punched or otherwise cut from the container sheet 10 along a trim line 32 in order to define the engaging edge 26 on the depending rim of the container. As seen in FIG. 3, there is a space S separating the web W and the overlying seal sheet 16 between each container cavity C, C. As heretofore mentioned, if the containers C, C are cut from the sheet 10 along the lines 32, 32 as by a steel rule die or the like, the seal sheet 16 will be mutilated or torn loose from the container sheet 10 to destroy the sealed relationship therebetween.

In keeping with this invention, a step is incorporated which avoids this problem. That is, the seal sheet 16 is at least partially severed, as by being perforated, or it is fully severed along a line 34 (FIG. 3) over each transverse and longitudinal web W. Preferably, the seal sheet 16 is perforated or fully cut along a transverse line 34 over each transverse web W while the container sheet is at rest during intermittent movement through the thermoforming machine. The longitudinal perforations or cuts are accomplished, preferably, while the container sheet 10 and seal sheet 16 are in motion through the machine. Suitable cutting or perforating wheels or knives (not shown) are located over the machine for this purpose.

It has been found that when the seal sheet 16 is perforated or otherwise partially severed along transverse and longitudinal lines such as indicated at 34, the said seal sheet will be sufficiently weakened along said lines where it will not be mutilate or torn away from sealed engagement with the container sheet 10 when the said container sheet is punched or otherwise cut transversely and longitudinally along the lines 32, 32. The result here is that a sealed package is provided which is adapted to receive a reusable snap-on cover such as the cover 24. Further, the seal sheet 16 is cut far enough outwardly from the top edge of the container rim that an overhanging flap or tab is provided which facilitates removal of the seal sheet prior to initial use of the contents of the package or container.

lclaim:

l. The thermoforming method of making a sealed plastic container from a container sheet and a seal sheet so that the finished container is adapted to receive a snap-on reusable cover, the method including the steps of heating the container sheet to a thermoforming condition, drawing portions of the container sheet into a plurality of die cavities to form a plurality of container cavities each having a peripheral depending rim portion which is spaced from the rim portions of all adjacent container cavities, depositing the desired contents in the formed container cavities, applying the seal sheet over the top of the container sheet and heat sealing it to the container sheet around the periphery of each container cavity at the top of its depending rim portion, at least partially severing the seal sheet around each container cavity along lines which are substantially evenly spaced between rim portions of adjacent container cavities, and then separating the formed but connected containers by cutting through the container sheet closely adjacent the bottom of the depending rim portion around each container cavity and along pairs of lines which are laterally spaced from the lines along which the seal sheet was at least partially severed, each separated container being thus prepared to receive a snap-on cover in engagement with its rim.

2. The method defined in claim 1 wherein the container cavities are formed in the container sheet in longitudinal and transverse rows and the seal sheet is at least partially severed in intersecting longitudinal and transverse lines between the said rows, and the containers are severed from the container sheet in a punch cutting operation.

3. The method of claim 2 wherein the container cavities are generally rectangular in plan shape, the container sheet and the seal sheet after being connected by heat sealing are advanced intermittently in the longitudinal direction, and the seal sheet is fully severed at least in the longitudinal lines between rows prior to severing the containers from the container sheet. 

1. The thermoforming method of making a sealed plastic container from a container sheet and a seal sheet so that the finished container is adapted to receive a snap-on reusable cover, the method including the steps of heating the container sheet to a thermoforming condition, drawing portions of the container sheet into a plurality of die cavities to form a plurality of container cavities each having a peripheral depending rim portion which is spaced from the rim portions of all adjacent container cavities, depositing the desired contents in the formed container cavities, applying the seal sheet over the top of the container sheet and heat sealing it to the container sheet around the periphery of each container cavity at the top of its depending rim portion, at least partially severing the seal sheet around each container cavity along lines which are substantially evenly spaced between rim portions of adjacent container cavities, and then separating the formed but connected containers by cutting through the container sheet closely adjacent the bottom of the depending rim portion around each container cavity and along pairs of lines which are laterally spaced from the lines along which the seal sheet was at least partially severed, each separated container being thus prepared to receivE a snap-on cover in engagement with its rim.
 2. The method defined in claim 1 wherein the container cavities are formed in the container sheet in longitudinal and transverse rows and the seal sheet is at least partially severed in intersecting longitudinal and transverse lines between the said rows, and the containers are severed from the container sheet in a punch cutting operation.
 3. The method of claim 2 wherein the container cavities are generally rectangular in plan shape, the container sheet and the seal sheet after being connected by heat sealing are advanced intermittently in the longitudinal direction, and the seal sheet is fully severed at least in the longitudinal lines between rows prior to severing the containers from the container sheet. 